Mutual hover protection for touchscreens

ABSTRACT

Disclosed is a touch sensor and method for detecting a touch in a capacitive touchscreen application, wherein the touch sensor is capable of distinguishing between a finger hovering above the touch sensor and a touch from a stylus having a small contact surface area without having to adjust the sensitivity of the touch sensor. The touch sensor includes a first sensing electrode, a transmit electrode, and a second sensing electrode, wherein the second sensing electrode is positioned substantially around the perimeter of the inner circuitry (i.e., transmit electrode and first sensing electrode). A touch is detected by sensing changes in a first capacitance between the transmit electrode and first sensing electrode and a second capacitance between the transmit electrode and second sensing electrode. The changes in the first and second capacitances are compared to determine whether the changes in the capacitances are due to a finger hover or a touch.

FIELD OF THE INVENTION

The present disclosure generally relates to capacitive touchscreenpanels and, more particularly, to a touch sensor pattern for use incapacitive touchscreens.

BACKGROUND

Conventional touchscreen sensors are designed to detect a user touch,wherein the user touch is generally conveyed using a finger or a stylus.Many styli are designed with a small surface area for contacting thetouchscreen device. For example, a stylus may have a contact surfacearea of approximately 1 mm in diameter. A stylus having a small contactsurface area is more difficult to detect than a stylus having a largercontact surface area. Many conventional touchscreen devices compensatefor the difficulty of detecting a stylus having a small contact surfacearea by increasing the sensitivity of the touch sensors, for example, bydecreasing the capacitive detection threshold of the touch sensors.

Unfortunately, when the sensitivity of the touch sensors is increased,false touch detections also increase. Most commonly, false touchdetections occur when the user hovers a finger over a touch sensor, butdoes not actually touch the sensor and does not intend to touch thesensor. In some instances, a false touch detection can occur when thefinger is hovering 1-3 mm above the surface of the touchscreen. Becausesuch false touch detections are undesirable, a need exists in the artfor improved touch sensors for use in single layer and multi-layer stackconfigurations of capacitive touchscreens.

SUMMARY

The present disclosure provides a capacitive sensing structure,comprising: a first sensing electrode configured to sense a firstcapacitance and produce a first sense signal indicative of the sensedfirst capacitance; a transmit electrode positioned substantially arounda perimeter of the first sensing electrode; a second sensing electrodepositioned substantially around a perimeter of the transmit electrode,the second sensing electrode configured to sense a second capacitanceand produce a second sense signal indicative of the sensed secondcapacitance; and controller circuitry configured to receive the firstand second sense signals, to compare a change in the sensed firstcapacitance to a change in the sensed second capacitance, and to producean output signal indicative of a user touch based upon the comparisonbetween the change in the sensed first capacitance and the change in thesensed second capacitance.

In another embodiment, the present disclosure provides capacitivesensing circuitry, comprising: a capacitive sensing structure,comprising: a first sensing electrode configured to sense a firstcapacitance and produce a first sense signal indicative of the sensedfirst capacitance; and a transmit electrode; a second sensing electrodepositioned substantially around a perimeter of the capacitive sensingstructure, the second sensing electrode configured to sense a secondcapacitance and produce a second sense signal indicative of the sensedsecond capacitance; and controller circuitry configured to receive thefirst and second sense signals, to compare a change in the sensed firstcapacitance to a change in the sensed second capacitance, and to producean output signal indicative of a user touch based upon the comparisonbetween the change in the sensed first capacitance and the change in thesensed second capacitance.

In yet another embodiment, the present disclosure provides a method fordetecting a touch, the method comprising: applying a force signal to acapacitive sensing structure comprising a transmit electrode and a firstsensing electrode; sensing a first capacitance via the first sensingelectrode; generating a first sense signal indicative of the sensedfirst capacitance; sensing a second capacitance via a second sensingelectrode, wherein the second sensing electrode is positionedsubstantially around a perimeter of the capacitive sensing structure;generating a second sense signal indicative of the sensed secondcapacitance; comparing a change in the sensed first capacitance to achange in the sensed second capacitance; and generating an output signalindicative of a user touch based upon the comparison between the changein the sensed first capacitance and the change in the sensed secondcapacitance.

The foregoing and other features and advantages of the presentdisclosure will become further apparent from the following detaileddescription of the embodiments, read in conjunction with theaccompanying drawings. The detailed description and drawings are merelyillustrative of the disclosure, rather than limiting the scope of theinvention as defined by the appended claims and equivalents thereof.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments are illustrated by way of example in the accompanyingfigures not necessarily drawn to scale, in which like numbers indicatesimilar parts, and in which:

FIG. 1 illustrates a conventional touch sensor pattern for use in acapacitive touchscreen;

FIG. 2 illustrates a first example embodiment of a touch sensor patternfor use in a capacitive touchscreen application in accordance with thepresent disclosure;

FIG. 3 illustrates an alternate embodiment of the touch sensor patternof FIG. 2 shown in a multilayer stack configuration;

FIG. 4 illustrates a second example embodiment of a touch sensor patternfor use in a capacitive touchscreen application in accordance with thepresent disclosure;

FIGS. 5A, 5B, and 5C illustrate a cross-sectional view of the touchsensor illustrated in FIG. 4;

FIG. 6 illustrates an example embodiment of the controller circuitry;

FIG. 7 illustrates a flow diagram illustrating a method in accordancewith the present disclosure;

FIG. 8 illustrates a flow diagram illustrating a method in accordancewith the present disclosure; and

FIG. 9 illustrates an alternate embodiment of a touch sensor having thefirst sensing electrode positioned between the transmit electrode andthe second sensing electrode.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure provides a touch sensor and method for detectinga small contact surface area without incurring a false touch detectionresulting from a user's finger hovering over the touch sensor. In otherwords, the disclosed touch sensor and method are capable ofdistinguishing between a finger hovering above the touch sensor and atouch from a stylus having a small contact surface area without havingto adjust the sensitivity of the touch sensor.

Reference is now made to FIG. 1, which illustrates an example embodimentof a conventional touch sensor 100 having a sensing electrode 102 and atransmit electrode 104. In operation, the touch sensor 100 receives aforce signal applied to the transmit electrode 104. A capacitance existsbetween the transmit electrode 104 and the sensing electrode 102. Atouch applied to the touch sensor 100 results in a change in thecapacitance between the transmit electrode 104 and the sensing electrode102. This capacitance change is used to detect the user touch.

For example, in the embodiment illustrated in FIG. 1, the capacitancebetween the transmit electrode 104 and the sensing electrode 102 has aninitial value when there is no touch. When a stylus having a contactsurface area of 1 mm (referred to herein as a “1 mm stylus”) contactsthe touch sensor 100 at location 106 above the sensing electrode 102,the capacitance between the transmit electrode 104 and the sensingelectrode 102 experiences a capacitance change that is substantialenough to recognize the touch (for example, by exceeding somecapacitance change threshold). Similarly, when the 1 mm stylus contactsthe touch sensor 100 at a location 108 above the transmit electrode 104,the capacitance between the transmit electrode 104 and the sensingelectrode 102 again experiences a substantial enough of a change to berecognized as a touch. Thus, a 1 mm stylus touch practically anywhere onthe touch sensor 100 causes a substantial enough of a capacitance changeto indicate a touch on the touch sensor 100.

Although the conventional touch sensor 100 is capable of detecting atouch with a 1 mm stylus, the sensor 100 also detects a touch when afinger is hovering approximately 1-3 mm above the sensor 100. Forexample, a finger having an approximate contact surface area of 7 mm,and hovering approximately 1 mm above the touch sensor 100, is capableof triggering a capacitance change that is similar to the capacitancechange caused by the actual touch of the 1 mm stylus. As such, it isdifficult to distinguish between a 1 mm stylus touch and a fingerhovering over the touch sensor 100 using the embodiment illustrated inFIG. 1.

The following description is directed to a touch sensor and method fordetecting a touch that are capable of distinguishing between a fingerhovering above the touch sensor and a touch from a stylus having a smallcontact surface area without having to adjust the sensitivity of thetouch sensor. In essence, the disclosed touch sensor incorporates asecond sensing electrode positioned substantially around a perimeter ofthe existing touch sensor circuitry (i.e., the transmit electrode andfirst sensing electrode). A first capacitance exists between the firstsensing electrode and the transmit electrode, and a second capacitanceexists between the second sensing electrode and the transmit electrode.In some embodiments, a change in the first capacitance is compared to achange in the second capacitance. When the difference between the changein the first capacitance and the change in the second capacitance islarge enough, the touch sensor indicates a touch detection. Otherwise,it does not. In other embodiments, the first capacitance is compared tothe second capacitance. When the difference between the firstcapacitance and the second capacitance is large enough, the touch sensorindicates a touch detection. Otherwise, it does not.

Reference is now made to FIG. 2, which illustrates an example embodimentof a touch sensor 200 for use in detecting a touch in a capacitivetouchscreen application, wherein the touch sensor 200 is capable ofdistinguishing between a finger hovering above the touch sensor 200 anda touch from a stylus having a small contact surface area without havingto adjust the sensitivity of the touch sensor 200. The touch sensor 200includes a first sensing electrode 202, a transmit electrode 204, and asecond sensing electrode 206. In the embodiment illustrated in FIG. 2,the first sensing electrode 202 includes a plurality of fingerstructures 208 interdigitated with finger structures 210 of the transmitelectrode 204. The second sensing electrode 206 is positionedsubstantially around the perimeter of the transmit electrode 204. Inthis context, substantially refers to at least 90% of the perimeter ofthe transmit electrode 204. To accommodate a single-layer touchscreenconfiguration, or a configuration where the first and second sensingelectrodes are on the same layer, the pattern of the second sensingelectrode 206 includes an opening 212 to allow for electricalconnections to the transmit electrode 204 and/or first sensing electrode202.

The example touch sensor 200 illustrated in FIG. 2 includes a first setof gaps 203 between each of the interdigitated finger structures 208 and210. The touch sensor 200 also includes a gap 205 between the transmitelectrode 204 and the second sensing electrode 206. In accordance withthe example embodiment illustrated in FIG. 2, the gaps 203 are 0.2 mm,the gap 205 is 0.3 mm, the finger structures 208 have a width w1 of 0.3mm, the finger structures 210 have a width w2 of 0.8 mm, and the secondsensing electrode 206 has a width w3 of 0.6 mm. It should be appreciatedthat these measurements are not intended to be limiting, but areprovided as an example.

In operation, controller circuitry (not shown) applies a force signal tothe transmit electrode 204. A first capacitance exists between thetransmit electrode 204 and the first sensing electrode 202, and a secondcapacitance exists between the transmit electrode 204 and the secondsensing electrode 206. The first and second capacitances each have aninitial, steady state value when there is no touch. As a stylus orfinger approaches the touch sensor 200, the first and secondcapacitances are affected by the approaching object. Specifically, asthe object approaches the second sensing electrode 206, the secondcapacitance changes, and as the object approaches the first sensingelectrode 202, the first capacitance changes.

Accordingly, the respective first and second capacitances (or thechanges in the respective first and second capacitances) are indicativeof the location of the approaching object with respect to the firstsensing electrode 202 and the second sensing electrode 206. When thefirst capacitance (or change in the first capacitance) is greater thanthe second capacitance (or change in the second capacitance), the objectis closer to the first sensing electrode 202 than it is to the secondsensing electrode 206. Conversely, when the second capacitance (orchange in the second capacitance) is greater than the first capacitance(or change in the first capacitance), the object is closer to the secondsensing electrode 206 than it is to the first sensing electrode 202.Thus, a touch may be determined by considering the respective first andsecond capacitances (or changes in the respective first and secondcapacitances) in view of the known locations of the first and secondsensing electrodes 202 and 206 in the touch sensor 200. Moreover, alarger object, such as a finger, hovering above the touch sensor 200 maybe distinguished from a touch from a stylus having a small contactsurface area without having to adjust the sensitivity of the touchsensor 200.

For example, in the embodiment illustrated in FIG. 2, the first sensingelectrode 202 is located toward the center of the touch sensor 200 andthe second sensing electrode 206 is located along the perimeter of thetouch sensor 200. Therefore, when the first capacitance (or change inthe first capacitance) is substantially greater (e.g., 20% greater) thanthe second capacitance (or change in the second capacitance), the touchobject (i.e., stylus or finger) is positioned closer to the center ofthe touch sensor 200 than it is to the perimeter of the touch sensor 200where the second sensing electrode 206 is located. When this conditionoccurs, the controller circuitry indicates detection of a user touch.

Conversely, when the second capacitance (or change in the secondcapacitance) is greater than the first capacitance (or change in thefirst capacitance), the touch object is positioned closer to theperimeter of the touch sensor 200 than it is to the center of the touchsensor 200. When this condition occurs, the controller circuitryindicates that there is no detection of a user touch, because the touchobject is located closer to the perimeter of the touch sensor 200 thanit is to the center of the touch sensor 200.

Similarly, when the first capacitance (or change in the firstcapacitance) is similar to the second capacitance (or change in thesecond capacitance), the controller circuitry indicates that there is nodetection of a user touch, because the touch object is not locatedsubstantially closer to the center of the touch sensor 200 than it is tothe perimeter of the touch sensor 200. This last condition is typicallyindicative of a finger hovering above the touch sensor 200.

Although the touch sensor 200 shown in FIG. 2 is illustrated as a sensorin a single-layer touchscreen application, the touch sensor 200 may beimplemented in a multilayer stack configuration. For example, thetransmit electrode 204 may comprise a first layer of the multilayerstack configuration, and the first sensing electrode 202 and secondsensing electrode 206 may comprise a second layer of the multilayerstack configuration. Alternatively, the first sensing electrode 202 andthe transmit electrode 204 may comprise a first layer of the multilayerstack configuration, and the second sensing electrode 206 may comprise asecond layer of the multilayer stack configuration. In such anembodiment, the second sensing electrode 206 may be positioned aroundthe entire perimeter of the transmit electrode 204 and may omit theopening 212. An example of such a configuration is illustrated in FIG.3.

FIG. 4 illustrates an alternate embodiment of a touch sensor 400 inaccordance with the present disclosure, wherein the touch sensor 400 iscapable of distinguishing between a finger hovering above the touchsensor 400 and a touch from a stylus having a small contact surface areawithout having to adjust the sensitivity of the touch sensor 400. Thetouch sensor 400 includes a first sensing electrode 402, a transmitelectrode 404, and a second sensing electrode 406. The embodimentillustrated in FIG. 4 is similar in function to that shown in FIG. 2,but instead provides a diamond shape. For example, the first sensingelectrode 402 is diamond-shaped and the transmit electrode 404substantially surrounds the perimeter of the first sensing electrode402. The second sensing electrode 406 substantially surrounds theperimeter of the transmit electrode 404.

In the embodiment illustrated in FIG. 4, the transmit electrode 404includes an open region 408 to allow for electrical connection to thefirst sensing electrode 402, and the second sensing electrode 406includes an open region 410 to allow for electrical connection to thefirst sensing electrode 402 and to the transmit electrode 404. The firstsensing electrode 402 and the transmit electrode 404 are separated by afirst gap 412. The transmit electrode 404 and the second sensingelectrode 406 are separated by a second gap 414. The embodiment of thetouch sensor 400 illustrated in FIG. 4 is shown in a single-layertouchscreen application. However, the touch sensor 400 may beimplemented in a multilayer stack configuration, in which case one ormore of the open regions 408 and 410 may be eliminated.

For example, the transmit electrode 404 may comprise a first layer ofthe multilayer stack configuration, and the first sensing electrode 402and second sensing electrode 406 may comprise a second layer of themultilayer stack configuration. In such an embodiment, the transmitelectrode 404 may be positioned around the entire perimeter of the firstsensing electrode 402 and may eliminate the open region 408.Alternatively, the first sensing electrode 402 and the transmitelectrode 404 may comprise a first layer of the multilayer stackconfiguration, and the second sensing electrode 406 may comprise asecond layer of the multilayer stack configuration. In such anembodiment, the second sensing electrode 406 may be positioned aroundthe entire perimeter of the transmit electrode 404 and may eliminate theopen region 410.

Operation of the touch sensor 400 is now discussed with reference toFIGS. 5A, 5B, and 5C, which illustrate a cross-sectional view of thetouch sensor 400 as viewed along line A-A of FIG. 4. In FIG. 5A, line504 indicates an electrical connection between the illustrated portionsof the transmit electrode 404, and line 506 illustrates an electricalconnection between the illustrated portions of the second sensingelectrode 406. It should be appreciated that the operation of the touchsensor 400 as illustrated and described with respect to FIGS. 5A, 5B,and 5C, is not limited to the sensor pattern 400 illustrated in FIG. 4,but may also be applied to other sensor patterns designed in accordancewith the present disclosure, including the touch sensor 200 illustratedin FIG. 2.

In operation, controller circuitry (not shown) applies a force signal502 to the transmit electrode 404. A first capacitance 508 existsbetween the transmit electrode 404 and the first sensing electrode 402,and a second capacitance 510 exists between the transmit electrode 404and the second sensing electrode 406. The first and second capacitances508 and 510 each have an initial, steady state value when there is notouch. As a stylus or finger approaches the touch sensor 400 (see FIGS.5B and 5C), the first and second capacitances 508 and 510 are affectedby the approaching object. Specifically, as the object approaches thesecond sensing electrode 406, the second capacitance 510 changes, and asthe object approaches the first sensing electrode 402, the firstcapacitance 508 changes. Accordingly, the respective first and secondcapacitances 508 and 510 (or the changes in the respective first andsecond capacitances 508 and 510) are indicative of the location of theapproaching object with respect to the first sensing electrode 402 andthe second sensing electrode 406. This information may be used to detecta touch.

When the first capacitance 508 (or change in the first capacitance 508)is greater than the second capacitance 510 (or change in the secondcapacitance 510), the object is closer to the first sensing electrode402 than it is to the second sensing electrode 406. Conversely, when thesecond capacitance 510 (or change in the second capacitance 510) isgreater than the first capacitance 508 (or change in the firstcapacitance 508), the object is closer to the second sensing electrode406 than it is to the first sensing electrode 402. Thus, a touch may bedetermined by considering the respective first and second capacitances508 and 510 (or the changes in the respective first and secondcapacitances 508 and 510) in view of the known locations of the firstand second sensing electrodes 402 and 406 in the touch sensor 400.Moreover, a larger object, such as a finger, hovering above the touchsensor 400 may be distinguished from a touch from a stylus having asmall contact surface area without having to adjust the sensitivity ofthe touch sensor 400.

For example, the embodiment illustrated in FIG. 5B shows a 1 mm stylus512 touching the touch sensor 400 at the first sensing electrode 402.Due to the size of the stylus 512 and the location of its touch, thestylus touch causes a substantial change in the first capacitance 508(shown in FIG. 5B as changed first capacitance 508′) with minimal impacton the second capacitance 510. As shown in FIG. 5B, when the firstcapacitance 508 (or change in the first capacitance 508) issubstantially greater (e.g., 20% greater) than the second capacitance510 (or change in the second capacitance 510), the touch object ispositioned closer to the center of the touch sensor 400 than it is tothe perimeter of the touch sensor 400 where the second sensing electrode406 is located. When this condition occurs, the controller circuitryindicates detection of a user touch.

In contrast, when a finger 514 is hovering over the touch sensor 400, asshown in FIG. 5C, the first capacitance 508 (or change in the firstcapacitance 508) (shown in FIG. 5C as changed first capacitance 508′) issimilar to the second capacitance 510 (or change in the secondcapacitance 510 (shown in FIG. 5C as changed second capacitance 510′).When this condition occurs, the controller circuitry considers thecapacitance changes to be occurring as a result of a finger hover and,as such, indicates that there is no detection of a user touch.

Reference is now made to FIG. 6, which illustrates an example embodimentof the controller circuitry 600. In the embodiment illustrated in FIG.6, the controller circuitry 600 includes circuitry 602 for generatingthe force signal 604. The controller circuitry 600 senses the firstcapacitance 606 at the first sensing electrode, and the secondcapacitance 608 at the second sensing electrode. The first capacitance606 is sensed at first capacitance-to-voltage converter circuitry 610,which includes an operational amplifier 612 and feedback capacitor Cf1,and produces a first voltage V1 indicative of the sensed firstcapacitance 606. Thus, as the first capacitance 606 changes, forexample, in response to a user touch, the first voltage V1 changesaccordingly. The second capacitance 608 is sensed at secondcapacitance-to-voltage converter circuitry 614, which includes anoperational amplifier 616 and feedback capacitor Cf2, and produces asecond voltage V2 indicative of the sensed second capacitance 608. Thus,as the second capacitance 608 changes, for example, in response to auser touch, the second voltage V2 changes accordingly. The first voltageV1 and second voltage V2 (or a change in the first voltage ΔV1 and achange in the second voltage ΔV2) can be used to detect a touch, asdiscussed in greater detail below.

The first voltage V1 and second voltage V2 are received at logiccircuitry 618. Upon start-up, the touch sensor, including controllercircuitry 600, achieves a steady state, whereby steady state values ofthe first capacitance 606 and second capacitance 608 are detected andrepresented as steady state values of the first voltage V1 and secondvoltage V2, respectively. In some embodiments, these steady statevoltage values are stored to be compared with real-time values of thefirst voltage V1 and second voltage V2. For example, the logic circuitry618 may sample the first and second voltages V1 and V2 to determine achange in the first voltage ΔV1 and a change in the second voltage ΔV2,wherein the changes are determined relative to the steady state valuesof the first voltage V1 and the second voltage V2.

In some embodiments, the changes in the first and second voltages ΔV1and ΔV2 are compared to determine whether a touch occurred.Specifically, the logic circuitry 618 compares the change in the firstvoltage ΔV1 to the change in the second voltage ΔV2 and indicatesdetection of a user touch when the change in the first voltage ΔV1 issubstantially greater than the change in the second voltage ΔV2. Forexample, in some embodiments, the logic circuitry 618 may indicate atouch when the change in the first voltage ΔV1 is approximately 20%greater than the change in the second voltage ΔV2.

Stated differently, the logic circuitry 618 determines the change in thefirst voltage ΔV1 relative to the initial value (steady state value) ofthe first voltage V1, and determines the change in the second voltageΔV2 relative to the initial value (steady state value) of the secondvoltage V2. The logic circuitry 618 then subtracts the second voltagechange ΔV2 from the first voltage change ΔV1. If the difference isgreater than a threshold value, then the logic circuitry 618 indicates atouch; otherwise, it does not. The threshold value may be selected to beany value. In some embodiments, however, the threshold is equal to 20%of the change in the second voltage ΔV2. In this embodiment, the logiccircuitry 618 indicates a touch when the change in the first voltage ΔV1is 20% greater than the change in the second voltage ΔV2.

In other embodiments, the logic circuitry 618 samples the instantaneousfirst and second voltage values V1 and V2, and then subtracts the secondvoltage V2 from the first voltage V1. If the difference is greater thana threshold value, then the logic circuitry 618 indicates a touch;otherwise, it does not. The threshold value may be selected to be anyvalue. In some embodiments, however, the threshold is equal to 20% ofthe second voltage V2. In this embodiment, the logic circuitry 618indicates a touch when the first voltage V1 is 20% greater than thesecond voltage V2.

The logic circuitry 618 produces an output signal 620 indicative ofwhether a touch was detected. The output signal 620 is received at hostcontroller circuitry 650, which is used to perform an operation inresponse to, or in consideration of, the output signal 620.

FIG. 7 illustrates a flow diagram 700 illustrating a method, inaccordance with the foregoing disclosure, for using a touch sensor todistinguish between a finger hovering above the touch sensor and a touchfrom a stylus having a small contact surface area without having toadjust the sensitivity of the touch sensor. At Block 701, a force signalis applied to a transmit electrode, thereby causing the first and secondcapacitances at the respective first and second sensing electrodes. AtBlock 702, the first capacitance is sensed using the first sensingelectrode. At Block 703, a first sense signal indicative of the sensedfirst capacitance is generated. At Block 704, the second capacitance issensed using the second sensing electrode. At Block 705, a second sensesignal indicative of the sensed second capacitance is generated. AtBlock 706, the first and second sense signals are sampled to determine achange in the first sense signal relative to the steady state value ofthe first sense signal and a change in the second sense signal relativeto the steady state value of the second sense signal. At Block 707, thechange in the second sense signal is subtracted from the change in thefirst sense signal. Block 708 determines whether the difference betweenthe changes in the first and second sense signals is greater than athreshold value (e.g., 20% of the change in the second sense signal). Ifthe difference between the changes in the first and second sense signalsis greater than the threshold value, then at Block 709, a signal isproduced indicating detection of a touch. Otherwise, at Block 710, asignal is produced indicating no touch was detected.

FIG. 8 illustrates a flow diagram 800 illustrating a method, inaccordance with the foregoing disclosure, for using a touch sensor todistinguish between a finger hovering above the touch sensor and a touchfrom a stylus having a small contact surface area without having toadjust the sensitivity of the touch sensor. At Block 801, a force signalis applied to a transmit electrode, thereby causing the first and secondcapacitances at the respective first and second sensing electrodes. AtBlock 802, the first capacitance is sensed using the first sensingelectrode. At Block 803, a first sense signal indicative of the sensedfirst capacitance is generated. At Block 804, the second capacitance issensed using the second sensing electrode. At Block 805, a second sensesignal indicative of the sensed second capacitance is generated. AtBlock 806, the first and second sense signals are sampled to determinethe instantaneous values of the first and second sense signals. At Block807, the second sense signal value is subtracted from the first sensesignal value. Block 808 determines whether the difference between thefirst and second sense signal values is greater than a threshold value(e.g., 20% of the second sense signal). If the difference is greaterthan the threshold, then at Block 809, a signal is produced indicatingdetection of a touch. Otherwise, at Block 810, a signal is producedindicating no touch was detected.

It should be appreciated that other touch sensor designs may beimplemented other than those illustrated and described herein. Forexample, the touch sensor may implement other sensor patterns other thanthose having interdigitated fingers or diamonds. Such alternateembodiments may also include those in which the first sensing electrodeis positioned between the transmit electrode and the second sensingelectrode.

For example, FIG. 9 illustrates such an embodiment of a touch sensor 900having a first sensing electrode 902 positioned between a transmitelectrode 904 and a second sensing electrode 906. The embodimentillustrated in FIG. 9 further includes controller circuitry 908. As withthe embodiments discussed herein, the controller circuitry 908 applies aforce signal 910 to the transmit electrode 904 to generate a firstcapacitance 912 using the first sensing electrode 902, and a secondcapacitance 914 using the second sensing electrode 906. The controller908 receives from the first sensing electrode 902 a first sense signal916 indicative of the first capacitance 912, and receives from thesecond sensing electrode 906 a second sense signal 918 indicative of thesecond capacitance 914. The controller circuitry 908 compares thechanges in the sense signals 916 and 918 to determine a touch detectionin accordance with the foregoing disclosure.

The foregoing description has provided by way of exemplary andnon-limiting examples a full and informative description of one or moreexemplary embodiments of this invention. However, various modificationsand adaptations may become apparent to those skilled in the relevantarts in view of the foregoing description when read in conjunction withthe accompanying drawings and the appended claims. However, all such andsimilar modifications of the teachings of this invention will still fallwithin the scope of this invention as defined in the appended claims.

For example, in some embodiments, the first sensing electrode andtransmit electrode may be considered a single capacitive sensingstructure that is capable of operating independent from the secondsensing electrode. In such embodiments, the second sensing electrode ispositioned substantially around the perimeter of the capacitive sensingstructure. In other embodiments, the transmit electrode and secondsensing electrode may be considered a single capacitive sensingstructure that is capable of operating independent from the firstsensing electrode. In such embodiments, the first capacitive sensor ispositioned along an interior of the capacitive sensing structure, andthe second sensing electrode is positioned substantially around theperimeter of the transmit electrode.

The foregoing sensor and method may be incorporated in multiple touchsensor types including, for example, zero-dimensional sensors,one-dimensional sensors, two-dimensional sensors, and wheel sensors.

What is claimed is:
 1. A capacitive sensing structure, comprising: afirst sensing electrode configured to sense a first capacitance andproduce a first sense signal indicative of the sensed first capacitance;a transmit electrode positioned surrounding at least 90% of a perimeterof the first sensing electrode; a second sensing electrode positionedsurrounding at least 90% of a perimeter of the transmit electrode, thesecond sensing electrode configured to sense a second capacitance andproduce a second sense signal indicative of the sensed secondcapacitance; and controller circuitry configured to receive the firstand second sense signals, to generate a first voltage indicative of thesensed first capacitance and generate a second voltage indicative of thesensed second capacitance, to sample the first and second voltage, todetermine a change in the sensed first capacitance by subtracting aninstantaneous value of the first voltage from a sampled value of thefirst voltage to produce a first changed voltage, to determine a changein the sensed second capacitance by subtracting an instantaneous valueof the second voltage from a sampled value of the second voltage toproduce a second changed voltage, to compare the change in the sensedfirst capacitance to the change in the sensed second capacitance, and toproduce an output signal indicative of a user touch based upon thecomparison between the change in the sensed first capacitance and thechange in the sensed second capacitance.
 2. The capacitive sensingstructure of claim 1, wherein the output signal is indicative of theuser touch when the change in the sensed first capacitance is greaterthan the change in the sensed second capacitance.
 3. The capacitivesensing structure of claim 1, wherein the output signal is indicative ofthe user touch when the change in the sensed first capacitance is 20%greater than the change in the sensed second capacitance.
 4. Thecapacitive sensing structure of claim 1, wherein a change in the firstvoltage is indicative of a change in the sensed first capacitance, and achange in the second voltage is indicative of a change in the sensedsecond capacitance.
 5. The capacitive sensing structure of claim 1,wherein comparing the change in the sensed first capacitance to thechange in the sensed second capacitance comprises: subtracting thesecond changed voltage from the first changed voltage to produce avoltage difference; and comparing the voltage difference to a thresholdvoltage.
 6. The capacitive sensing structure of claim 5, wherein thethreshold voltage is 20% of the second changed voltage.
 7. Capacitivesensing circuitry, comprising: a capacitive sensing structure,comprising: a first sensing electrode configured to sense a firstcapacitance and produce a first sense signal indicative of the sensedfirst capacitance; a transmit electrode; a second sensing electrodepositioned surrounding at least 90% of a perimeter of the capacitivesensing structure, the second sensing electrode configured to sense asecond capacitance and produce a second sense signal indicative of thesensed second capacitance; and controller circuitry configured toreceive the first and second sense signals, to generate a first voltageindicative of the sensed first capacitance and to generate a secondvoltage indicative of the sensed second capacitance, to sample the firstand second voltages, to determine a change in the sensed firstcapacitance by subtracting an instantaneous value of the first voltagefrom a sampled value of the first voltage to produce a first changedvoltage, to determine a change in the sensed second capacitance bysubtracting an instantaneous value of the second voltage from a sampledvalue of the second voltage to produce a second changed voltage, tocompare the change in the sensed first capacitance to the change in thesensed second capacitance, and to produce an output signal indicative ofa user touch based upon the comparison between the change in the sensedfirst capacitance and the change in the sensed second capacitance. 8.The capacitive sensing circuitry of claim 7, wherein the output signalis indicative of the user touch when the change in the sensed firstcapacitance is greater than the change in the sensed second capacitance.9. The capacitive sensing circuitry of claim 7, wherein the outputsignal is indicative of the user touch when the change in the sensedfirst capacitance is 20% greater than the change in the sensed secondcapacitance.
 10. The capacitive sensing circuitry of claim 7, whereinthe transmit electrode is positioned around a perimeter of the firstsensing electrode.
 11. The capacitive sensing circuitry of claim 7,wherein the first sensing electrode is positioned around a perimeter ofthe transmit electrode.
 12. The capacitive sensing circuitry of claim 7,wherein a change in the first voltage is indicative of a change in thesensed first capacitance, and a change in the second voltage isindicative of a change in the sensed second capacitance.
 13. Thecapacitive sensing circuitry of claim 7, wherein comparing the change inthe sensed first capacitance to the change in the sensed secondcapacitance comprises: subtracting the second changed voltage from thefirst changed voltage to produce a voltage difference; and comparing thevoltage difference to a threshold voltage.
 14. The capacitive sensingcircuitry of claim 13, wherein the threshold voltage is 20% of thesecond changed voltage.
 15. A method for detecting a touch, the methodcomprising: applying a force signal to a capacitive sensing structurecomprising a transmit electrode and a first sensing electrode; sensing afirst capacitance via the first sensing electrode; generating a firstvoltage indicative of the sensed first capacitance; sensing a secondcapacitance via a second sensing electrode, wherein the second sensingelectrode is positioned surrounding at least 90% of a perimeter of thecapacitive sensing structure; generating a second voltage indicative ofthe sensed second capacitance; sampling the first and second voltages;determining a change in the sensed first capacitance by subtracting aninstantaneous value of the first voltage from a sampled value of thefirst voltage to produce a first changed voltage; determining a changein the sensed second capacitance by subtracting an instantaneous valueof the second voltage from a sampled value of the second voltage toproduce a second changed voltage; comparing the change in the sensedfirst capacitance to the change in the sensed second capacitance; andgenerating an output signal indicative of a user touch based upon thecomparison between the change in the sensed first capacitance and thechange in the sensed second capacitance.
 16. The method of claim 15,wherein the output signal is indicative of the user touch when thechange in the sensed first capacitance is greater than the change in thesensed second capacitance.
 17. The method of claim 15, wherein theoutput signal is indicative of the user touch when the change in thesensed first capacitance is 20% greater than the change in the sensedsecond capacitance.
 18. The method of claim 15, wherein the transmitelectrode is positioned around a perimeter of the first sensingelectrode.
 19. The method of claim 15, wherein the first sensingelectrode is positioned around a perimeter of the transmit electrode.20. The method of claim 15, wherein comparing the change in the sensedfirst capacitance to the change in the sensed second capacitancecomprises: subtracting the second changed voltage from the first changedvoltage to produce a voltage difference; and comparing the voltagedifference to a threshold voltage.
 21. The method of claim 20, whereinthe threshold voltage is 20% of the second changed voltage.